To address the molecular interactions between ionic liquids (ILs) such as trimethylammonium acetate [(CH3)(3)NH][CH3COO] (TMAA), trimethylammonium hydrogen sulphate [(CH3)(3)NH][HSO4] (TMAS). trimethylammonium dihydrogen phosphate [(CH3)(3)NH][H2PO4] (TMAP) and triethylammonium dihydrogen phosphate [(CH3CH2)(3)NH][H2PO4] (TEAP) with N-methyl-2-pyrrolidone (NMP), density (rho), ultrasonic sound velocity (u) and viscosity (eta) measurements have been performed across the entire concentration range and the wide temperature range from 298.15 to 313.15 K in steps of 5K under ambient pressure. Further, on the basis of the measured properties, excess volumes (V-E), isentropic compressibility deviations (Delta kappa(s)) and viscosity deviations (Delta eta) were obtained for all these systems under the same experimental conditions. The results are correlated by the Redlich-Kister type equation. The results are also analysed on anion dependent phenomena and temperature influence on measured and derived properties of ILs with NMP mixtures. A qualitative analysis of molecular interactions between ILs and NMP is discussed in terms of the ion-dipole, ion-pair interactions, and hydrogen bonding. (C) 2012 Elsevier B.V. All rights reserved.